1. Field of the Invention
The present invention relates to an imaging apparatus, more specifically, to an improvement in the imaging apparatus provided with two auto focusing devices for carrying out auto focusing operations of mutually different kinds.
2. Description of the Prior Art
Conventionally, an imaging apparatus such as a still camera or a video camera is provided with an auto focusing (AF) device for adjusting a focusing of an image of a subject in optimum.
The AF device in a conventional still camera or the like for recording the image of the subject to a recording medium such as a film of video tape and so on, so-called an outside light AF operation such as an active AF which moves a photographic optical system such as a focus lens to a focusing position corresponding to an obtained distance obtained by calculating the distance to the subject based on a time taking for a reflected wave to return from the subject by projecting a near-infrared ray or an ultrasound wave or the like for example to the subject, or a passive AF which moves the photographic optical system such as the focus lens to the focusing position corresponding to the obtained distance obtained by calculating the distance to the subject based on a phase contrast, have been applied.
In the imaging apparatus (there may be an occasion referred to as a digital camera appropriately hereunder) which projects the image of the subject to an imaging device such as a CCD or the like and takes out the projected image as an electric signal, the AF operation can be carried out based on the image of the subject that actually imaged to the imaging device through the focus lens or the like since the image can be taken out as an image signal substantially simultaneously to projection of the image.
That is to say, in the AF operation, the contrast (including a sharpness of the image) of the image signal obtained by the imaging device is evaluated in real time in every movement of the focus lens or the like while moving the focus lens or the like, and the movement of the focus lens or the like is stopped at the position where a value which is evaluated becomes maximum. This is referred to as a CCDAF operation or a contrast AF operation.
The CCDAF operation has an advantage that a focusing accuracy is extremely high since it is the AF that carries out the AF operation by evaluating the image that is actually projected to the imaging device.
On the other hand, there is a problem that it takes a long time to complete the AF operation when a repeating frequency of successive operations which include accumulation of image, transfer, computation of evaluated value and comparison are increased.
Consequently, the time taking from starting to completion of the AF operation, more specifically, a time-lag gravely influences the focusing of the image of the subject in such a circumstance that photographing the subject that moves at a high speed, and as the AF operation is not completing, there is an occasion that the photographing cannot be performed in a desired timing.
Also, since the CCDAF operation evaluates the actual image of the subject, there is an occasion that an appropriate focusing operation cannot be carried out in a circumstance that the entire contrast is low.
On the contrary, although the aforementioned outside light AF operation is inferior to the CCDAF operation in terms of the focusing accuracy, it is possible to follow effectively to a dynamic subject and to prevent photograph timing from losing since the above mentioned time-lag is small.
In addition, the outside light AF operation has an advantage that it is generally hard to be influenced by the contrast of the subject as the outside light AF operation measures based on an arrival time of the reflected wave when performing its AF operation by projecting the near-infrared ray or the like.
In this connection, there is proposed an imaging apparatus having two AF devices which are an outside light AF device for carrying out the outside light AF operation and the CCDAF device and a CCDAF device for carrying out the CCDAF operation capable of switching over by a selection of either of the AF operations alternatively in corresponding to a photographing situation or a situation of the subject (Japanese Patent Laid Open such as No. 2001-255456).
But, according to the above art, a user invariably has to carry out a prior selecting operation when selecting either of the AF operations in a case of choosing either of them.
That is to say, when photographing the dynamic subject, it is necessary to carry out the photographing after setting a photographing mode to a time-lag priority mode (focusing speed priority mode) that corresponds to the outside light AF operation by operating a dial for switching over the photographing mode or a switching button or the like beforehand, and on the other hand, when photographing the image that the focusing accuracy is called for, it is necessary to carry out the photographing after setting the switching button or the like to a focusing accuracy priority mode that corresponds to the CCDAF before photographing.
For example, during the photographing in the focusing accuracy priority mode, when the dynamic subject is suddenly appeared in sight and trying to take the photograph of it, at first the user has to carry out the selecting operation of the photographing mode so as to change over the AF operation to the time-lag priority mode.
Consequently, there has been a problem that the desired image cannot be obtained due to the loss of photographing timing by a hesitation in the switching operation of the mode or lose sight of the subject by adverting the user's eyes from the subject in order to carry out the switching operation.
Therefore, the applicant has proposed an imaging apparatus capable of changing over the AF operation appropriately with in a range of a normal photographing operation (Japanese Patent Application No. 2002-175297).
This imaging apparatus is provided so as to automatically change over the outside light AF operation or the CCDAF operation corresponding to an operating time in which the user has taken for a pressing operation from a half-pressed position to a full-pressed position of a release button.
That is to say, when the user presses the release button throughout the entire stroke from an initial position to the full-pressed position continuously at once (hereunder it is called at-once pressing), the operating time taking from the half-pressed position which is set at a middle part of the entire stroke to the full-pressed position is extremely short, therefore the outside light AF operation with the time-lag priority is selected since such operation represents the user's intension that wishes to release the shutter quickly.
On the other hand, when the user once stops the pressing operation at the half-pressed position and then pressed to the full-pressed position, the time taking for the pressing operation from the half-pressed position to the full-pressed position is long and correspondingly the CCDAF operation with the focusing accuracy priority is selected since such operation represents the user's intension that wishes to carry out the focusing carefully by performing a focus locking at the half-pressed position.
According to the proposed art, the user can instantaneously change over the two kinds of AF operations by the operation within the normal photographing operation for pressing the shutter release button so that the loss of photographing timing or erroneously photographing the image that the focusing accuracy is low can be avoided.
By the way, according to the above proposed art by the present applicant, it simply changes over the AF operation by an elapsed time taking from a half-pressed to a full-pressed, therefore how to set a threshold value (criterion time, reference time) to the elapsed time is important in the actual photographing situation.
For example, it can be conceived to set the time taking from starting of the outside light AF operation to completion of the outside light AF operation by the half-pressing of the shutter release button as the above mentioned criterion time.
In this instance, when the shutter release button is fully-pressed during the operation of the outside light AF operation (elapsed time<criterion time or elapsed time≦criterion time), the performing of the photographing is performed soon after the operation of the outside light AF operation is completed since it can be considered that the intention of the quick photographing performing is called for, and when the shutter release button is fully-pressed after the outside light AF operation is completed (criterion time≦elapsed time or criterion time<elapsed time) the performing of the photographing is carried out by switching from the outside light AF operation to the CCDAF operation since it can be considered that the photographing performing is not in a hurry.
But, an initial position of the focus lens at the time the shutter release button is half-pressed and the outside light AF operation starts is not always in a regular position in every photographing, where a stopped position of the last photographing performing becomes the initial position of the current photographing. In addition, since a focusing position as a moving target position that is calculated by the outside light AF operation varies in every time corresponding to a distance value to the subject, the time required from starting of the outside light AF operation (initial position) to the completion of the operation (focusing position) varies in every photographing.
Consequently, if the time from starting of the outside light AF operation to its completion is set as the above mentioned criterion time, this criterion time varies in every photographing and therefore it can be considered that it may being set extremely short time beyond the user's prediction.
Furthermore, in such a case as above mentioned, even if the user has pressed the shutter release button at once such as the half-pressing and then to the full-pressing by the intention of selecting the outside AF operation, there is likely that the function automatically becomes changed to the CCDAF operation against the user's intention.
In addition, in the actual photographing circumstance, there may be cases that further pressing of the shutter release button is ceased even though the half-pressing operation of the shutter release button is performed, or the circumstance may have changed to such a photographing circumstance that the quick shutter release is wished during the CCDAF is in operation even though once having intentionally operated to select the CCDAF operation.